1. Field of the Invention
This invention pertains to scavenging of power by virtue of human-carried or human-borne devices.
2. Related Art and Other Considerations
It would be highly beneficial if human energy (that would otherwise be wasted) could be scavenged and stored for useful purposes, such as powering electronic devices. For example, a human walking at a normal pace of three mph produces a power output of 233 Watts. Thus, there is a considerable amount of energy that is potentially available to scavenge and use.
There has been considerable interest in the possibility of scavenging human power and either using it directly, or storing it for later use, to power electronic devices. While the interest in the feasibility of this concept was initially generated by the military to power an assortment of electronic equipment carried by a soldier in the field, recent interest in powering portable, personal electronic devices, such as cell phones and MP3 players, is beginning to see interest. See, for example, U.S. Patent Publication 2001/0035723 wherein electroactive polymer devices are used to generate electrical energy by converting mechanical energy generated during by heel strikes during walking into electrical energy.
To date, the problems with scavenging human energy have been summed up in several reports issued by the U.S. United States Office of Naval Research (ONR) and the United States Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO). Thus far, ONR and DARPA DSO have found such devices to date to have one or more of low power output, to be overly complex and/or bulky, and not to be cost effective.
As an example, FIG. 1 shows a previously suggested device for scavenging human power through the up-and-down motion of the contents in a backpack. The modified backpack of FIG. 1 consists of a series of springs that allow the contents of the backpack to bounce up and down during walking. The bouncing cargo of the FIG. 1 backpack is directly coupled to a linear gear which in turn drives a small, conventional rotary generator. It is claimed that the FIG. 1 backpack can produce up to 7 Watts of power from the up-and-down motion of the contents of an 85 lb pack during normal walking. The FIG. 1 backpack concept device is described, e.g., at http:/news.nationalgeographic.com/news/2005/09/0908—050908_backpack.html. See also U.S. Patent Publication 20040183306 and U.S. patent application Ser. No. 10/803112, filed Mar. 17, 2004.
Several problems with the FIG. 1 type of scavenging device are evident. The first is that the scavenging equipment is fairly complex. It also adds 10 lbs to the weight of the backpack, which is obviously undesirable as this directly translates into a decreased load carrying capacity. This is certainly an important issue in military applications. Another issue is that the up-and-down motion of the pack contents could lead to fatigue of the carrier, or even loss of balance. Again this is an important issue, particularly in military applications.
Piezoceramic devices have also been suggested to scavenge footfall energy, energy available from limb motion, and respiratory energy. However, a problem arises with using piezoceramic devices to scavenge energy—fragility of the ceramic itself.
What is needed, therefore, and an object of the present invention, is a human-carried piezogenerator device which is sufficiently rugged to scavenge energy.